In scintillation cameras used in medical imaging, it is known to integrate the light intensity signals generated by a planar array of photodetectors in response to scintillation light produced in a scintillator optically coupled to the photodetectors. The integrated intensity signals are used as energy signals in the computation of the scintillation event's total energy and the scintillation events positions within the scintillator for the purposes of accurate image construction.
In recent years, position calculation in scintillation cameras has started to be implemented using digital computers and the integrated intensity signals from the photodetectors have been converted to digital energy values using analog-to-digital converters connected to an integrator associated with each photodetector. Such a system is illustrated in U.S. Pat. No. 5,309,357 in which integrators receive photodetector intensity signals which are delayed by an appropriate period of time required able to determine whether the sum signal of all light intensity signals is indicative of a valid scintillation event. A valid scintillation event is determined to be one in which the light produced by the scintillator corresponds to an energy of a photon emitted by a particular radioactive isotope ingested or applied to the medical patient being imaged. This is typically done by analyzing a sum signal of all light intensity signals from the photodetectors. Such a system is known from U.S. Pat. No. 5,270,547.
In the circuitry described in U.S. Pat. No. 5,309,357, integration and analog-to-digital conversion is carried out in one of two ways. In the first way, integration and analog-to-digital conversion is only carried out on a group of the delayed intensity signals after it has been determined that there has been a valid scintillation event in the camera during a time frame in which the group had a substantial signal. In the second way, all light intensity signals are integrated and then converted into a serial digital format each time a valid event in the camera is detected.
In the known art, multiple events, i.e. two or more scintillations occurring with overlapping time frames, cause problems or complications in data processing in the camera. The camera circuitry must be designed with a view to clearly identify valid events and produce integration energy signals which are accurate and free from interference. When the energy signals include interference, the resulting image produced by the scintillation camera will be flawed or blurred.
Multiple events also complicate the process of valid event discrimination. For example, when a first event occurs in one portion of the scintillator, and then within the same time frame another event begins elsewhere in the scintillator, the valid event discriminator must determine whether the double peak multiple event includes a valid event.